Need expert help for secret...

I can say that I'm an expert of Kingdom Hearts. I've completed everything I can on the game on expert (yes, everything) and I was just busy getting items for Power Up synthesis in Hollow Bastion when I noticed a chest I had not reached before in the lower dungeon area. I also noticed that in the waterway where the blue switches move the walls, there are more blue switches just out of reach. How do I get to these blue switches? Does anyone know how to get to the platform above the bubble that leads to the switch that opens the front door (the one you press with Beast)? (if you look up, you'll see a platform with another blue switch next to it - how do we get to that platform?). On the outside lower level where you're walking on the water surrounded by the ice, there is an entrance to the waterway that leads to seemingly nothing. What can be done in this dead-end hallway? I think all of these questions are connected - solving one will solve the others. Is there something simple that I missed, or is it impossible to reach the other blue switches in the moving-wall area? Please help - this is driving me insane :(

I've noticed this too and I would also like to know. Unfortunately, I don't think it's possible.

. . . and to be clear, you have actually beaten the game, right?
You're just on an old save looking for some extra stuff to do, right?
'Cause otherwise, if you're talking about completing Hollow Bastion (getting to the Maleficent battles) then would actually be pretty simple.

Try using the magic Gravija, or something along those lines.

Chests floating out of reach can be brought to the ground with Gravity/Gravira/Graviga magic. Chests beyond reach near the bubbles are slightly more tricky. Bubbles are air in water. Water (HOH) forms a crystaline solid at temperatures below 32 degrees Farenheit, 0 degrees Celsius, or 273 Kelvin. In other words, freeze the frelling bubble. It forms a platform you can stand on. But it only lasts for a short time, for the solidified water will melt eventually...